Electrode for electric discharge devices



Aug. '30, 1927.

- 1,640,428 F. SKAUPY ET AL ELECTRODE FOR ELECTRIC. mscmmes DEVICES Filed Oct. 50, 1923 Fig.2. 9

Inventors? Franz Skaupg,

Marce I I0 Pirani,

FI-i-tz Bahr, Werner- Fehse,

. Their 3 H: tor-ne Patented Aug. 30,1927.

UNITED STATES FRANZ SKAUPY, MARCELLO I PIRANI, FRITZ BARR, AND WERNER FEHSE, OF BERLIN, GERMANY, ASSIG-NORS TO GENERAL ELECTRIC COMPANY, A. CORPORATION 03' new YORK.

Application filed October 30, 1923, Serial No.

The present invention relates to the manufacture and construction of non-consuming electrodes of concentrated mass for electric arc lamps or similar electric discharge de- 5 vices.

Heretofore tungsten electrodes of concentrated mass, such as used for example in lamps or similar devices in'which an arc is operated ina gas. have been made by fusing 1 the lower end of a piece of tungsten wire held in a vertical position until a spherical molten drop of tungsten is formed at the heated end of the wire. Since aheavy drop of tungsten easil breaks off it has been possible to obtain y this process with stem wires of suitable size only comparatively small spherical electrodes, say about 3.5 to 4 m. m. in diameter. The spherical electrode bodies often have hollow spaces in the interior which are formed at the high temperature of fusion by the evaporation of small amounts of impurities present in even the best purified tungsten. The hollow spaces in the electrodes are harmful as they tend to produce inequalities of temperature in the electrode bodies and decrease the length of life of the arc electrode.

According to the process constituting the present invention, electrodes of refractory 80 metal of which tungsten is an example, are made from powdered metal which first is partially "consolidated. by compression and preliminary sintering, then is joined to a supporting stem and is finally further consolidated by heating to high incandescence in an inert environment. The shrinking of the electrode body upon the stem according to this process produces a most intimate and firm connection between the stem and the body. The resulting electrodes are dense 671,795, and in Germany December 22, 1922.

form, preferably somewhat larger than the dimensions desired in the finished article. It is not necessary in our process to adhere to a spherical shape, in fact it is advanta- 5 geous to produce hemispherical electrode bodies having a flat surface, as shown in Fig.

1. An electrode of this shape has the advantage that when lamps containing the same are used in projectors for motion pictures or the like, the total light radiation is concentrated on the film to be projected. The pressed electrodes are next given a preliminary sintering operation by heating to a temperature sufficiently high to partially consolidate the metal, (say, a temperature of 1300). This firing treatment renders the bodies sufiiciently hard to be worked mechanically. If desired, the shape of the electrodes may be changed by mechanical means and the smoothness of the surface improved. At this stage of manufacture a hole is mechanically made in the electrodes, as by boring and a supporting stem, also consisting of tungsten, molybdenum, or other refractory material, preferably of wrought metal, is inserted loosely in the depression in the electrode body before the final sintering stem. The stem. of the electrode may to advantage be inserted obliquely as shown in $0 the drawing. This shape of electrode prevents creeping up of the arc from the electrdde itself to the supporting stem. The final step in the manufacture of the electrodes consists in sintering at bright incandescence (to a temperature of about 3000), in order to completely consolidate the electrode mass 1, and to shrink the same upon the relatively thin inserted stem 2. Although this final step may be carried out in any suitable device, it may to advantage be carried out in a tube furnace, as shown in Fig. 2 of the drawing. This furnace as diagrammatically indicated comprises a c lindrical tank a, which is closed at the lower end by a mercury packing 7), contained within a channel in a plate p. The two water cooledcurrent supply conductors 0, d, project through the base plate p into the interior. The current conductor a is con- IN nected to a small tank 6 containing mercury, in the interior of which is mounted a cooling coil f. Into this body of mercury projects a terminal 9 of a tube h, preferably consisting of tungsten.

The terminal 5 conveniently is constituted of hinged jaws held in firm relation to the tube 72. by a spring 8. The tube h is held at the opposite end by a. clamp terminal 2', attached to the current supply conductor (1.

The partially sintered electrode bodies 70 provided as above described with inserted stems, are placed within the heater tube h,

thelow eiend of which is closed in any suitable manner, as for example, by means Of a wad of tungsten'wlre. The tank a during the sintering operation is supplied with hydrogen, which enters by a tube 'm and leaves the tank through a tube n. The tungsten tube h is heated to incandescence by the passage of current. The inserted electrodeslc aresintered by radiated heat and become firmly united with the support ing stems. After the completion of the sintering process the electrodes may be directly mounted in lamps 01' other electric discharge What we claim as new and desire to secure by Letters Patent of the United States, is

refractory metal which consists in compressing powdered refractory metal to desired form, sintering to partially consolidate the same. inserting a stem and completing the consolidation by sintering at a higher temperature.

2. The method of making electrodes of tungsten which consists in pressing powdered tungsten to desired form, partially consolidating at an elevated temperature, inserting a stem and completing the consolidation by heating the article to a higher The method of making electrodes of temperature below the fusion temperature of tungsten.

3. An electrode comprising a mass of sin.- tcred refractory metal having a flat surface and a relatively thin stem of wrought metal oblique to said surface and imbeddcd in and united with said sintered mass.

In witness whereof, we have hereunto so our hands this 8th day of October, 1923.

FRANZ SKAUPY. MARCELLO PIRANI. FRITZ BAHR.

WERNER FEHSE. 

